The present invention relates to tools for setting fasteners and more particularly to nose assemblies for installing pull type fasteners. Examples of such nose assemblies are shown in U.S. Pat. No. 3,107,806 issued Oct. 22, 1963 to Van Hecke et al for "Modified Nose Assembly", U.S. Pat. No. 4,347,728, issued Sep. 7, 1982 to Smith for "Apparatus And System For Setting Fasteners", U.S. Pat. No 5,119,554 issued Jun. 9, 1992 to Wilcox for "Pintail Ejector Assembly For Fastener Installation Tooling", and U.S. Pat. No. 5,146,773 issued Sep. 15, 1992 to Rosier for "Tapered Rotatable Offset Nose Assembly". As can be seen these nose assemblies are utilized in conjunction with a hydraulic and/or pneumatic power source for installing two piece fasteners by applying a relative axial pulling force, for example, between a pin or mandrel and a collar or sleeve. Examples of swage type fasteners, or lockbolts, employing a pin and collar and adapted to be set with a relative axial pulling force are shown in the '728 Smith patent, supra, U.S. Pat. No. 4,324,518, issued Apr. 13, 1992 to Dixon for "Dish Compensating Flush Head Fastener", and U.S. Pat. No. 5,090,852, issued Feb. 25, 1992 to Dixon for "High Strength Fastener And Method". Examples of blind type fasteners employing a pin and a sleeve and adapted to be set by a relative axial pulling force are shown in U.S. Pat. No. 4,627,775 issued Dec. 9, 1986 to Dixon for "Blind Fastener With Grip Compensating Means", U.S. Pat. No. 4,844,673, issued Jul. 4, 1989 to Kendall for "Lock Spindle Blind Bolt With Lock Collar Providing Pin Stop Support" and U.S. Pat. No. 4,863,325, issued Sep. 5, 1989 to Smith for "Two Piece Blind Fastener With Lock Spindle Construction". With both the swage and blind type fasteners, the pin has an elongated shank provided with a pintail or pull portion having a plurality of pull grooves adapted to be gripped by a plurality of chuck jaws in the nose assembly. The chuck jaws are normally resiliently biased towards a closed condition for engagement with the pull grooves such that, upon insertion of the pintail portion into the nose assembly and actuation of the tool, the pull grooves will be gripped by the chuck jaws. At the same time, however, in the deactuated condition, the chuck jaws will be normally held open against the resilient bias to facilitate insertion of the pintail portion into the aperture defined by the opened chuck jaws as well as ejection of the pintail portion after the fastener has been set.
An anvil member is adapted to engage the collar or sleeve, depending upon the type of fastener, and, upon actuation of the tool, the chuck jaws, as noted, are biased to their closed condition to grip the pintail portion of the pin shank and a relative axial pulling force is then applied between the engaged members of the fastener by way of the relative axial force between the chuck jaws and the anvil. Typically the pin or mandrel is also provided with a weakened portion or breakneck groove which is located on the shank of the pin between the pull or pintail portion and the remainder of the shank and is adapted to fracture at a preselected axial load, i.e. pin break load, after the fastener has been set. This results in a finally installed fastener having a generally flush and/or compact structure with minimal or no pintail protrusion.
The magnitude of the pin break load required to fracture the breakneck groove, however, can result in the transmission of significant reaction or shock loads to the nose assembly and more particularly to its internal structure including the chuck jaws and the resilient bias mechanism. The magnitude of pin break load can be especially high with swage type fasteners since the breakneck groove must be of sufficient strength to withstand the high installation loads required for the anvil to swage the collar onto the pin.
It has been a common practice in nose assembly designs to use a metal coil type spring to provide the resilient bias for actuating the chuck jaws (see '554 patent to Van Hecke, supra). The same spring, however, also fully receives the shock loads resulting from pin break. The continued, repetitive application of the shock load to the coil spring can result in wear and/or eventual reduction or loss of bias whereby the proper operation of the nose assembly could be impaired. On the other hand, a significant portion of the shock load, if not absorbed, may be transmitted to the operator.
In order to reduce the shock load experienced by the operator, nose assemblies were constructed using an elastomeric structure comprising a series of O-rings which were packed together to provide the resilient biasing action as well as an improved shock absorbing function; see for example the U.S. Pat. No. 3,446,509, issued May 27, 1969 to Colosimo for "Chuck Jaw", U.S. Pat. No. 3,534,580, issued Oct. 20, 1970 to Chirco for "Eccentric Riveting Tool", and U.S. Pat. No. 3,605,478, issued Sep. 20, 1971 to Chirco for "Integral Anvil Holder". In such constructions, however, the elastomeric material could be responsive to changes in temperature whereby the resilient bias force and shock absorbing resistance could vary. Also the build up of contamination and/or dirt could impair the operation of the O-ring assembly while, at the same time, the continuous, repetitive loading of the O-ring members could also eventually result in a reduction of the desired resilient bias applied to the chuck jaws.
Still another approach utilizes a combination of O-ring members and a coil spring placed in a series or aligned orientation. With this type of structure the coil spring is adapted to provide most of the resilient bias for the operation of the chuck jaws while the O-ring structure is adapted to provide most of the shock load absorption. With this series construction, however, the spring is substantially compressed and/or bottomed out in response to the full force of the pin break or shock load; thus, again, the problem of wear on the coil spring as a result of the heavy loads and changes in the load capability of the O-ring with temperature fluctuations could still result in undesired wear and functional variations.
Examples of installation tools with other shock absorbing constructions can be seen in the U.S. Pat. No. 4,878,372, issued Nov. 7, 1989 to Port et al for "Shock-Absorbing Fluid-Actuated Fastener Installation Tool" and U.S. Pat. No. 4,964,292, issued Oct. 23, 1990 to Kaelin et al for "Shock-Absorbing Fluid-Actuated Pressure System".
The present invention provides a nose assembly having a unique design in which a coil spring and assembly of O-ring members are utilized in a generally parallel combination in which the coil spring and O-ring members function substantially separately. In this construction the resilient bias required for the routine opening and closing function of the chuck jaws is provided substantially solely by the coil spring structure while the elastomeric O-ring members are used to provide substantially all of the shock or pin break load absorption with the coil spring being subject only to a small portion of the overall pin break load.
In addition the nose assembly of the present invention utilizes a unique construction in which dirt and debris introduced into the forward, open portion of the assembly is automatically expelled reducing the frequency with which the nose assembly has to be cleaned.
Thus it is an object of the present invention to provide a unique construction for a nose assembly for an installation for setting pull type fasteners.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.